1. Field of the Invention
This invention relates to the field of expandable tubulars and more specifically to a method and apparatus for running downhole tubulars of a diameter smaller than the size of the casing already installed in the wellbore and expanding the tubular to a larger diameter downhole.
2. Background of the Invention
Expandable tubulars have become a viable technology for well drilling, repair, and completion. In one technique, the expandable tubular string has a pre-expanded portion (e.g., expansion swage launcher) at the bottom of the string with the expansion swage inserted in the launcher. Hydraulic pressure may be applied through a drill pipe to an area below the expansion swage to generate a force for propagation of the swage through the tubular and subsequent expansion of the tubular. One drawback of this technique is the safety aspect of the operation at the end of the expansion process. For instance, when the expansion swage is exiting from the expanded tubular (e.g., “pop-out” point), the entire volume of expanded tubular may be under the high pressure, and the tubular may be radially and longitudinally stretched by the pressure. The expandable tubular string typically employed may have a length of several thousand feet and may be expanded by applying three thousand to five thousand pounds per square inch of pressure. The combined energy of the compressed liquid and of the elastically stretched tubular, when instantly released at the pop-out point, may propel the drill pipe with the expansion swage acting as a piston out of the well causing equipment damage and injuries to the rig personnel.
Another technique includes an expansion device having an expansion cone, an actuator capable of displacing the expansion cone, and two end anchors capable of preventing movement of the actuator when the expansion cone is displaced. A drawback of this device is that it may not reset automatically. For instance, the repeated steps of application and withdrawal of hydraulic pressure to the whole system, including drill pipe, are time consuming, uneconomical in operation, and not suitable for expanding long tubulars. Techniques have been developed to overcome such drawbacks. For instance, techniques include an expansion device that includes an expansion cone, an actuator, two or three anchoring devices as well as a sliding valve that may automatically reset the actuator. The sliding valve may be positioned in an annular chamber of a double-walled cone-guide shaft. In addition, the sliding valve may be displaced between a front position, in which the valve passage is at the front side of the actuator piston, and a rear position, in which the valve passage is at the rear side of the actuator piston. Drawbacks to such a design include that the valve does not provide passage for the liquid out of the chamber on one side of the piston when the pressure is applied in the chamber on the other side of the piston, which may create a pressure lock and make the actuator in-operational. Further drawbacks include that the modification of such valve design, in order to incorporate fluid passage out from one side of the actuator piston and pressure fluid entering on the other side of the actuator piston simultaneously, may be difficult because the sliding valve provides communication with high pressure line only.
Therefore, there is a need for a safe and efficient technique of tubular radial expansion in downhole conditions.